The hot-carrier relaxation dynamics of Cd3As2 thin films has been investigated by using femtosecond pump-probe spectroscopy in a transmission geometry. A comparative study of degenerate and non-degenerate experiments reveals that hot-carrier distribution in Cd3As2 is established with a time constant of around 400 fs. We employ the quantum transport equation to calculated the cooling of hot carriers in 3D Dirac materials mediated by both acoustic and optical phonons.

The terahertz optical response of a commensurate topologically insulator(TI)-graphene eterostructure is also investigated. The interplay of interlayer hopping and topological band structure leads to additional selection rules for the inter band optical transition. The optical conductivity of such a system exhibits interesting features that do not occur in the two constituent surfaces separately. The transitions between TI bands give rise to resonant peaks in conductivity and transitions between the TI bands and the graphene bands give rise to a nonresonant conductivity.

Professor Chao Zhang received his PhD in physics in 1987 from City University of New York, USA. From 1987 to 1989, he was a postdoctoral fellow at Max-Planck-Institute for Solid Research in Stuttgart, Germany, working on quantum magneto-transport in semiconductor nanostructures. From 1989 to 1992, He was a research associate at Canada’s Meson Research Facility in Vancouver, working on quantum coherence and dissipation in solids. From 1993, he has been a tenured faculty member in the School of Physics, University of Wollongong, Australia. Currently he is a senior professor of physics. From 2004-2014, he served as the associate director of the Institute of Superconducting and Electronic Materials. He is a Fellow of Australian Institute of Physics. He is the associate editor of Frontier of Optolelectronics and a member of the editorial board of Scientific Report. His research interest is in the areas of quantum transport of nanostructures, terahertz photonics, nonlinear dynamics of semiconductors, graphene and topological insulators. He has published around 200 papers in refereed journals with an H-index of 30. He has received many awards including Norwegian Research Council Fellowship (1990), Norwegian Research Council Senior visiting fellowship (1996), JSPS senior fellowship (2002), and Australian Academy of Science International Award (2000, 2004).